This application addresses broad Challenge Area (03): Biomarker Discovery and Validation and specific Challenge Topic, 03-ES-101: Validation of New Exposure Assessment Methodologies. Despite evidence of widespread dietary exposure among children and adults, little is currently known about dietary exposure of infants to pesticides. This project will address the current gap in knowledge by validating methods for measuring current use pesticides in breast milk and infant formula. Although the breast milk method will be pilot tested on samples collected from a birth cohort in Thailand, it will have broad applications for the U.S. population. Because these pesticides are widely distributed in the food supply, all U.S. infants are potentially exposed. A valid method for measuring these compounds in breast milk and formula would have a major impact on our ability to evaluate pesticide exposures in early life, contributing to an improved understanding of their longer-term health effects. PUBLIC HEALTH RELEVANCE: Little is known about the dietary exposures of infants to pesticides, despite their vulnerability to chemical insults and despite evidence of widespread dietary exposure among older children and adults. This project will address the current gap in knowledge by validating methods for measuring pesticides in breast milk and infant formula. Such methods would have a major impact on our ability to evaluate pesticide exposures in early life, contributing to an improved understanding of their longer-term health effects.